The majority of wind turbines utilize a mechanical speed increasing gearbox which is prone to failure resulting in extended down time and high maintenance costs. It is possible to remove the gearbox from the wind turbine system by utilizing a hydrostatic transmission. These prior art wind turbines have generally been limited to fixed speed generators in order to enable the system to be attached to a power grid. This has been accomplished using blade control systems to compensate for changes in wind speed, pressure control systems to control changes in hydraulic flow, as well as variable displacement motors and pumps to compensate for pressure changes in the hydrostatic systems.
The use of power electronics to convert a variable frequency output of a variable speed AC generator into useable AC power is well known. U.S. Pat. No. 5,083,039 deals with this type of control used on variable speed wind turbines.
It would therefore be an advantage to provide a variable speed wind turbine that utilizes a hydrostatic transmission that does not require the use of a gearbox.